1. Field of the Invention
The present invention relates to a seal for a liquid chromatography column.
2. Related Art and Prior Art Statement
A liquid chromatography column comprises a plurality of carefully sized particulate through which a liquid is filtered. The particulate, often times silica, is formed into a filter bed and retained within a column which is capped at each end with a porous device known as a frit or more specifically as a filter bed frit. The filter bed frits are held in place by column end fittings or caps which appropriately mount to each column end. Liquid is forced, usually through tubing, at high pressure into one column end fitting, through a filter bed frit, through the filter bed, out the second filter bed frit, and finally exiting out the second column end fitting. A sealing means, commonly an o-ring or gasket is used to seal each column end fitting to the column. To allow for a more uniform dispersal of the liquid, some mechanism is typically provided between the filter bed frit and the column end fitting which is designed to divert the liquid over the entire filter bed frit. One manner of accomplishing this dispersal is to machine grooves into the column end fitting at the surface facing the filter bed frit. These grooves are intended to provide a path for distribution of the liquid over the entire surface area of the filter bed frit. Another option is to use a disperser. The disperser, essentially another frit, spreads the liquid evenly across the filter bed frit by providing a number of pores arranged in a pattern over the entire surface area of the disperser frit. These pores are designed to allow the liquid to pass with minimal interference. A combination of the disperser frit and grooved end fittings are also utilized. Frequently when a disperser frit is used, the column is sealed with double o-rings at each end. The first or interior o-ring is designed to stop the majority of the leakage and the second o-ring stops whatever liquid may have escaped the first.
The field of liquid chromatography can be subdivided into two major classifications or categories. The first utilizes a preparatory column and the second, an analytical column. Preparatory columns are used for processing large amounts of liquid by quickly stripping the incoming liquid stream of some of its constituent chemical components. The outcoming liquid stream is further separated by preparatory columns until a relatively pure liquid results. Once a satisfactory purity has been reached with the liquid stream, the stream is placed into an analytical column. The analytical column works identically to the preparatory column but processes a much smaller quantity of liquid. Where the preparatory column acts as a bulk separator, the analytical column separates specific components out of the stream resulting in a very high degree of purity. However, oftentimes to create large quantities the reverse is true as well. An analytical column is first used to establish the constituents of the filter bed best suited to extract a particular liquid stream. Once the bed is identified it is scaled upwards and used in a preparative column in order to perform bulk separation to more rapidly process the liquid stream and obtain larger quantities of the desired end product.
As important as these chromatography columns are to many emerging scientific and technical fields, the current design is subject to numerous problems and deficiencies. One major problem associated with chromatography columns pertains to the use of o-rings. The use of o-rings forms a limitation to the column""s operating pressure which is approximately 3000-4000 psi. Typically o-rings are manufactured from neoprene which is not resistant to the chemicals these units often see. To increase their chemical resistivity, the o-ring is often encased in teflon. The teflon, however, does not possess the same elastic qualities that make neoprene a desirable o-ring. O-rings manufactured in this manner simply do not function sufficiently well to enable the use of higher pressures and thus higher outputs. Not only do the o-rings need to function properly but in order for the column to remain sealed at these pressures, proper alignment must exist between each of the internal components, that is, the filter bed frit, the disperser frit, and the interior and exterior o-rings if a double o-ring system is used.
The problem associated with sealing the columns becomes even more troublesome since the processing of the liquid oftentimes requires that the column be continuously replaced during use. The technician still must replace the column when it is desirable to separate different components from the stream or when the column is spent. This process though not technically a difficult job, requires proper tooling, some care, and a significant quantity of time to assemble the column correctly to ensure that the column does not leak under high pressure. An analytical column though often disposed of when spent, often times utilizes a threaded fitting and requires the use of wrenches to install and remove. Frequent replacement requires a significant expenditure of time on the part of the technician better utilized elsewhere.
Preparative columns, on the other hand, are often reused. These columns are frequently provided with threaded fasteners to secure the end fitting to the column. In order to maintain a leak-free operating status, these fasteners are torqued to a significant load. As the filter bed is replaced and the column reused, the fasteners are subjected to a recurring cyclical load as they are first torqued and subsequently removed over and over again. This cyclical loading increases the likelihood of failure due to fatigue. Another problem, associated more often with double o-ring systems, is that it has been found that liquid leaks between the two o-rings forming a dead volume which reduces the effectiveness of the column, wastes a portion of the liquid sample and could even be hazardous as this dead volume of liquid is spilled when the column is removed from the system.
What is needed is a liquid chromatography column capable of quick replacement and substitution. The desired column would exhibit features enabling it to be simple to replace, easy to obtain a proper seal capable of withstanding 8000-10,000 psi pressures which will result in increased column throughput and sample processing time, while eliminating a number of internal components and eliminating the potential for a dead liquid volume.
In view of the above, it is an object of the invention to provide a liquid chromatography seal which is simple in structure, low in cost, wherein seal leakage and failure is low, which is self-seating and seals without excessive force creating a leak-proof seal capable of withstanding pressures in excess of 8000 psi.
It is another object of the present invention to provide a chemically resistant seal without the disadvantages inherent to o-ring type seals.
Yet another object of the present invention is to provide a seal which increases the longevity of the column by reducing the forces associated with cyclical torquing of the fasteners.
Still another object of the present invention is to provide a single seal structure which serves to seal the column and disperse the liquid to the frit.
According to the invention, there is provided a liquid chromatography seal which in lieu of o-rings utilizes a series of sealing surfaces each disposed upon a single seal device. The physical construct of the seal device is dependent upon whether it is used in a flanged column or a threaded fitting type column. The first type is associated with preparative columns and the latter is associated with analytical type columns. The common element between the different configurations is the use of an angled seal. The angled seal, comprises an annular ring which in cross-section forms three separate contiguous sealing surfaces which in combination effectively seal the column against any leakage. Furthermore the seat upon which the seal is configured to rest is shaped to receive the seal in mated relation. To ensure a leak-proof seal, it is desirable for the chromatography seal to exhibit some characteristics of plastic deformation.
As the end cap is secured to the column, the seal is forced into its seat thus minimizing the chances for liquid to escape through the seal. Further, since alignment of the internal components goes a long way towards establishing a proper seal, the seal itself effectively serves to disperse the liquid over the surface of the filter frit. The seal replaces the o-ring in a preparative column and since no disperser geometry is necessary, it eliminates the disperser frit as well as the double o-ring seal. This reduction in parts not only resolves some of the sealing problems associated with current designs but also simplifies the device as well. When the seal is constructed in this fashion, elimination of dead volume and enabling the column to withstand pressures in excess of 8000 to 10,000 psi with a very low torque load are the results.